This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Fischer 344, adult male rats need cardiac gated microCT data, ~10-12 frames, and MRI - Strain MRL/lpr (autoimmune prone) The rapid growth in genetics and molecular biology combined with the development of techniques for genetically engineering small animals has led to increased interest in in vivo small animal imaging. With the rise of small animal imaging, new instrumentation, data acquisition strategies, and image processing and reconstruction techniques are being developed and researched. A major challenge is how to evaluate the results of these new developments. One method from which to evaluate and improve medical imaging devices and image processing techniques is through the use of simulation studies. An important aspect of simulation is to have a realistic phantom or model of the subject's anatomy and physiological functions from which imaging data can be generated using accurate models of the imaging process. The advantage in using such phantoms in simulation studies is that the exact anatomy and physiological functions are known, thus providing a gold standard from which to evaluate and improve imaging devices, data acquisition techniques and image processing and reconstruction methods. Currently, there is a lack of realistic computer generated phantoms modeling the rat anatomy and physiological functions for use in molecular imaging research. The purpose of the study is to develop a realistic and flexible 4D digital rat phantom, including cardiac and respiratory motions, and investigate its usefulness in molecular imaging research. The 3D anatomy of the rat will be based on MRI data of an adult male Fischer 344 rat with an isotropic resolution of 50 microns. A 4D model for the cardiac motion will be based on cardiac-gated microCT data of a similar rat. Respiratory motion will be incorporated into the phantom based on known respiratory mechanics. The rat phantom developed in this work will be distributed for academic research purposes to investigate the development and optimization of small animal imaging devices and techniques.